The figures compare with an average audience of 6.1 million-7.9 million for crime drama Ripper Street, whose first season ended earlier this year, and more than 8 million for the second season of Sherlock.

The White Queen, a 10-episode co-production with Starz, has a summer run on the BBC flagship channel. The series is set to premiere in the U.S. on Starz on Aug. 10. The period drama is set during the so-called War of Roses in England, the 15th-century conflict between rival factions for the English throne.

Based on the best-selling historical novels in Philippa Gregory's The Cousins' War series, the show is produced by Britain’s Company Pictures. It stars Max Irons (Red Riding Hood), Rebecca Ferguson, Amanda Hale (Ripper Street), James Frain (The Tudors) and Janet McTeer.

Filmed in Belgium with a budget of more than $15 million, The White Queen has been endorsed by new BBC director general Tony Hall. Last month, he called the show the kind of "really ambitious" drama that the British public broadcaster should bring to viewers.